You can use Activity Monitor (in /Applications/Utilities) to see what processes are taking the most CPU and Memory, and monitor disk input and output. This may help to identify what is causing the slowness.

However, the most likely cause is the presence of an internal mechanical hard drive, either by itself or as part of a 'Fusion' drive.

Mechanical hard drives are much slower than modern 'solid state' SSDs. If your Mac has to 'swap' memory data to and from the disk, then this will slow things down dramatically.

While taking an iMac apart to replace the drive may be of moderate difficulty, you would do better to use an external SSD. Old Thunderbolt 2 enclosure are harder to find these days, but even a USB3 SSD will be faster.

Apple continued to install hard drives in iMacs for many years after it was using SSDs in its other Macs. So, in answer to the question 'is this normal for an iMac', the answer is sadly, yes.

You can use Activity Monitor (in /Applications/Utilities) to see what processes are taking the most CPU and Memory, and monitor disk input and output. This may help to identify what is causing the slowness.

However, the most likely cause (in the absence of any other info) is the presence of an internal mechanical hard drive, either by itself or as part of a 'Fusion' drive.

Mechanical hard drives are much slower than modern 'solid state' SSDs. If your Mac has to 'swap' memory data to and from the disk, then this will slow things down dramatically. Also, the drive is at the end of its useful lifespan, and may show signs of failing.

While taking an iMac apart to replace the drive may be of moderate difficulty, you would do better to use an external SSD. Old Thunderbolt 2 enclosure are harder to find these days, but even a USB3 SSD will be faster.

Apple continued to install hard drives in iMacs for many years after it was using SSDs in its other Macs. So, in reply to the question 'is this normal for an iMac', the answer is sadly, yes.